使用 SwiftUI 观察窗口大小调整事件

Question

我目前有这样的

LazyVGrid

设置：

struct NetworkGrid: View {
    var networks: [Network]
    let columns = [
            GridItem(.flexible()),
            GridItem(.flexible()),
            GridItem(.flexible()),
            GridItem(.flexible())
        ]
    
    var body: some View {
        ScrollView {
            LazyVGrid(columns: columns) {
                ForEach(networks) { network in
                    NetworkCard(network: network)
                }
            }
        }
    }
}

我想根据当前窗口大小设置网格列数，即

func windowDidResize(_ notification: Notification) {
    itemWidth = CGFloat(300)
    if window.width <= itemWidth {
        GridItem(.flexible()), GridItem(.flexible())
    } else if window.width <= itemWidth * 2 {
        GridItem(.flexible()), GridItem(.flexible()), GridItem(.flexible())
    } else if window.width <= itemWidth * 3 {
        GridItem(.flexible()), GridItem(.flexible()), GridItem(.flexible()), GridItem(.flexible())
    }
    ...
}

我将如何使用 SwiftUI 实现这样的观察者？

Answer 1

如果您想在调整视图大小时更新

@State

或

@ObservedObject

变量，可以使用 onAppear(perform:) 使用初始视图大小更新变量，并使用 onChange(of:perform:) 来检测视图大小变化：

struct MyView: View {
  @State private var size: CGSize = .zero

  var body: some View {
    GeometryReader { geometry in
      ZStack {
        Text("Hello World")
      }.onAppear {
        size = geometry.size
      }.onChange(of: geometry.size) { newSize in
        size = newSize
      }
    }
  }
}

Answer 2

相当于监听窗口大小的 SwiftUI 可能会使用

GeometryReader

。在您的示例中，您可以读取大小并根据其宽度读数动态决定列：

struct NetworkGrid: View {
    var networks: [Network]
    
    func columnsForWidth(width: CGFloat) -> [GridItem] {
        print("Columns for width: \(width)")
        return Array(repeating: GridItem(.flexible()), count: Int(width) / 100)
    }
    
    var body: some View {
        GeometryReader { geometry in
            ScrollView {
                LazyVGrid(columns: columnsForWidth(width: geometry.size.width)) {
                    ForEach(networks) { network in
                        NetworkCard(network: network)
                    }
                }
            }
        }
    }
}

Answer 3

无需 GeometryReader 也可以实现此目的：

let networkCardSize = 200

ScrollView(.vertical) {
    LazyVGrid(
        columns: [
            // Move an item across rows iff it has enough space
            // to contain *just* the item (+ padding).
            GridItem(.adaptive(minimum: networkCardSize, maximum: networkCardSize)
        ],
        alignment: .leading,
        spacing: 0
    ) {
        ForEach(networks) { network in
            NetworkCard(network: network)
                .padding(10)
        }
    }
}

spacing

没有按我的预期工作，但可能有一个很好的解决方案。我也不确定动态大小的元素在这里的表现如何。静态尺寸很棒！